<!DOCTYPE html>
<html>
<head>
  <script src="https://unpkg.com/konva@4.0.18/konva.min.js"></script>
  <meta charset="utf-8" />
  <title>Konva Brighten Image Demo</title>
  <style>
    body {
      margin: 0;
      padding: 0;
      overflow: hidden;
      background-color: #f0f0f0;
    }

    #slider {
      position: absolute;
      top: 20px;
      left: 20px;
    }
  </style>
</head>

<body>
<div id="container"></div>
<input id="slider" type="range" min="-1" max="1" step="0.05" value="0" />
<script>
  function loadImages(sources, callback) {
    var images = {};
    var loadedImages = 0;
    var numImages = 0;
    for (var src in sources) {
      numImages++;
    }
    for (var src in sources) {
      images[src] = new Image();
      images[src].onload = function() {
        if (++loadedImages >= numImages) {
          callback(images);
        }
      };
      images[src].src = sources[src];
    }
  }
  function buildStage(images) {
    var stage = new Konva.Stage({
      container: 'container',
      width: window.innerWidth,
      height: window.innerHeight
    });

    var layer = new Konva.Layer();

    var lion = new Konva.Image({
      image: images.lion,
      x: 80,
      y: 30,
      draggable: true
    });

    lion.cache();
    lion.filters([Konva.Filters.Brighten]);
    layer.add(lion);
    stage.add(layer);
    var slider = document.getElementById('slider');
    slider.oninput = function() {
      console.log('slider.value :   '+slider.value)

      lion.brightness(slider.value);
      layer.batchDraw();
    };
  }

  var sources = {
    lion: 'logo.png'
  };

  loadImages(sources, buildStage);
</script>
</body>
</html>
